This invention relates in general to liquid lubricated rolls. More specifically, it relates to a liquid lubricated roll that automatically recirculates the lubricant without an external power source and automatically controls the distribution and level of the lubricant along the roll.
Curved rolls are commonly used in processing paper, textiles and other sheet materials. They typically have a set of generally cylindrical hollow spools rotatable on antifriction bearings that are spaced along a stationary, curved axle. Generally, an elastomeric sleeve is pulled over the spools to place a continuous, smooth surface in contact with the sheet material.
Lubrication of the bearings is an important factor affecting life, reliability and performance of the roll. Conventional rolls lubricate the bearings by packing them with grease. This system, however, does not offer sufficient lubrication at very high speeds (e.g. 6,000 feet per minute FPM). Also, the lubricant cannot be conveniently replaced without a complete disassembly of the roll.
Lubrication by a liquid such as oil, in contrast, can provide excellent lubrication of the bearings at high speeds. Liquid lubricants, however, present a variety of other problems. First, the roll must include a system for directing the lubricant onto the bearings. One system described in U.S. Pat. No. 3,666,049 to Kern utilizes a number of spray nozzle fittings located within the roll adjacent the bearings. While the fittings do lubricate the bearings, they are costly, difficult to service, and require an external pressure source to force the lubricant through the fittings. If even one fitting should clog or otherwise malfunction, or if there is even a temporary failure in the pressurized supply of lubricant, the affected bearings will quickly become damaged or destroyed. Further, oil must constantly drain from the roll and the Kern lubrication system does not control condensation produced when the roll cools.
Another liquid lubrication system described in U.S. Pat. No. 3,746,129 to Knapp introduces a quantity of the lubricant to the interior of the roll from a standpipe. The centrifugal force of the rotating spools forces the lubricant against the interior surface of the spools to form a rotating annular body of liquid. Projections on the axle extend into the annular body of lubricant to produce a lubricating spray or mist. Passages in the spools that span the bearings allow an axial flow of the lubricant past the outer races of the bearings. One problem with a supply of lubricant inside the roll is that an excess of the lubricant can flood the bearings. Flooding is undesirable because it can heat and damage both the bearings and the lubricant and it requires an increased torque to turn the roll. To control this problem, Knapp employs four co-planar scoops that skim the liquid annulus. Each scoop has a separate drain line that feeds to a common drain pipe.
While this lubrication system functions well, it nevertheless has several shortcomings. When the roll stops, the lubricant collects at the low ends of the roll. On start up, this maldistribution floods the end bearings and insufficiently lubricates the central bearings. Moreover, the spool passages and the four scoops are relatively slow in establishing an even distribution of the lubricant at the proper level. Another problem is that there is no recirculation of the oil. Once the initial supply is distributed, no substantial quantity of lubricant is added or removed from the roll. If additional lubricant is simply poured into the standpipe while the roll is running, it floods the bearings. Thus, it is not feasible to add, drain or clean the oil during operation. Also, while a pressure build-up on the roll can vent through the standpipe, there is no system for controlling the formation of condensation as the roll cools.
U.S. Pat. No. 4,018,302, commonly assigned with the Knapp patent and this application, discloses barrier rings located adjacent the bearings which allow the lubricant to flow past the bearings when the roll is rotating. While these rings avoid flooding of the end bearings of a curved roll when the roll stops, they do not provide recirculation of the lubricant and to some extent they restrict the axial redistribution and overall level control of the lubricant.
It is therefore a principal object of this invention to provide a high speed, liquid lubricated roll with a recirculation system for the lubricant that does not require an external power source.
Another object is to provide such a roll with the capability to add, drain and clean lubricant and to control the flow rate of the lubricant.
A further object of the invention is to provide a curved liquid lubricated roll that continuously lubricates each bearing without flooding at high speeds (i.e., above 1600 FPM).
Yet another object is to provide such a curved roll that rapidly distributes the lubricant along the roll to all of the bearings and controls the level of the lubricant throughout the roll.
Still another object of the invention is to provide a roll with a liquid lubricant recirculation, distribution and leveling system that relieves pressure differences in the roll as it heats and cools and restricts the formation of condensation in the roll.
A still further object is to provide a liquid lubricated roll with lubricant recirculation, distribution and leveling system that is independent of the speed and direction of rotation of the roll.
Another object is to provide a roll with the foregoing advantages that is reliable, comparatively easy to maintain and has a relatively long product life.